A fast quantitative modelling of ns laser ablation based on non-stationary averaging technique

Abstract

A semi-analytical approach to a quantitative analysis of thermal ns laser ablation is presented. The nonlinear heat equation is reduced to three ordinary differential equations for the surface temperature, spatial width of the enthalpy distribution, and the ablated depth. Due to its speed and flexibility, the method provides a convenient tool for the fast analysis of experimental data. The influence of different factors on ablation curves (ablated depth h vs. fluence φ) is studied. Analytical formulas for threshold fluence φ th and h( φ) dependences are discussed. The ablation curves reveal three regions of fluence: Arrhenius, linear, and the screening region. Small vaporization enthalpy results in a sub-linear but faster than logarithmic h( φ) dependence. Weakly-absorbing materials may exhibit two different ablation regimes – without or with ablation of the heated subsurface layer. The method is applied to the analysis of the single pulse ablation of polyimide. The single thermal evaporation energy ≈1.51 eV describes satisfactory the ablation at 248, 308 and 351 nm wavelengths.